BIOLOGY 5 Marks Questions

1. Primary structure – It is the linear sequence of amino acids in a polypeptide chain.
2. Secondary structure – The polypeptide chain is coiled to form a three-dimensional structure.
3. Tertiary structure – The helical polypeptide chain is further coiled and folded to form a complex structure.
4. Quaternary structure – More than one polypeptide chains assemble to form the quaternary structure.

1. The enzymes are generally proteins which are high molecular weight complex globular proteins. They can associate with non-protein substance for their activity.
2. The enzymes do not start a chemical reaction but only accelerate it. They combine temporarily with the substrate molecules and are not consumed or changed permanently in the reaction which they catalyse.
3. The enzyme controlled reactions are reversible.
4. The enzymes are specific in action. An enzyme catalyses only a particular kind of reaction or acts on a particular substrate only.
5. The enzymes are thermo labile i.e., heat sensitive and can function best at an optimum temperature. Similarly, enzymes show maximum activity at optimum pH.
6. The enzymes are inactivated by poisons and radiation.

1. Test for protein

Biuret’s test – If Biuret’s reagent is added to protein, then the colour of the reagent changes from light blue to purple.

2. Test for fats and oils

Grease or solubility test

3. Test for amino acid

Ninhydrin test – If Ninhydrin reagent is added to the solution, then the colourless solution changes to pink, blue, or purple, depending on the amino acid.

Yes. The biomolecules can be represented by the ball and stick model. The bonds which hold the atoms are represented by sticks, whereas the atoms are represented by balls.

Example: In the model of D-glucose, the oxygen atoms are represented by pink balls, the hydrogen atoms by green balls, while the carbon atoms are represented by grey balls.

Peptide bond is a covalent bond that joins the two amino acids by – NH – CO linkage.

Phosphodiester bond is a strong covalent bond between phosphate and two sugar groups. Such bonds form the sugar phosphate backbone of nucleic acids.

1. Double helix model of DNA (Walton-Crick model of DNA).
2. (A) 2 nm (B) 3.4 rim (C) 0.34 run.
3. The bonds between C and G are three.
4. This is B-form of DNA.
5. B-DNA is right-handed spiral structure.

1. Simple lipids– These are formed from fatty acids and alcohol. They do not have any additional group, e.g., fats, suberin, cutin, wax.
   1. Neutral or true fats– They are triglycerides which are formed by esterification of three molecules of fatty acids with one molecule of trihydric alcohol, glycerol (glycerine or trihydroxy propane). Three molecules of water are eliminated.fatty acids, e.g., dipalmito-stearin, palmito-oleio-stearin, steario-oleio-palmitin. In fats the three fatty acids are only rarely similar (e.g., tripalmitin, tristearin, triolein). They are called pure fats. Usually they are dissimilar or two of the three fatty acids are similar. They are known as mixed fats, e.g., Butter. Fats are named after the names of fatty acids, e.g., dipalmito-stearin, palmito-oleio-stearin, steario-oleio-palmitin.
      
   2. Waxes– They are fatty acid esters of long chain monohydric alcohols like cytyl, ceryl or mericyl.
      
   3. Cutin– It is a complex lipid produced by cross-esterification and polymerisation of hydroxy fatty acids, as well as other fatty acids with or without esterification by alcohols other than glycerol.
      
   4. Suberin– It is a mixture of fatty material having condensation products of glycerol and phellonic acid or its derivatives.
      
2. Compound or conjugated lipids: These are the esters of fatty acids and alcohol but contain other substances also, e.g., phosphor lipid, glycol lipids, sphingo lipids etc.
   1. Phospholipids- They are triglyceride lipids where one fatty acid is replaced by phosphoric acid which is often linked to ‘additional nitrogenous groups like choline (in lecithin), ethanolamine (in cephalin), serine or inositol.”
      
   2. Sphingo lipids– They are lipids having amino alcohol sphirigosine. Sphingomyelins contain an additional phosphate attached to choline like phospholipids.
      
   3. Glycol lipids– These are sugar containing lipids, in which the lipids portion of themolecule is usually based on glycerol or sphingosine and the sugar is typically galactose, glucose or inositol.
      
3. Derived lipids: These are lipid-like substance such as sterol or derivatives of lipids, e.g., steroids, prostaglandins and teapenes.
   1. Steroids– They are a group of complex lipids that possess a hydrogenated cyclopentano-perhydrophenanthrene ring system.
      
   2. Prostaglandins– They are derivatives of arachidonic acid and other 20 carbon fatty acids.
      
   3. Terpenes– They are lipid like hydrocarbons formed of isoprene (C₅H₈) units. Steroids like cholesterol are also derived from terpenes having 6 isoprene units. Fats are also differentiated into two main types, on the basis of their melting points at room temperature as follows. Hard Fats are solids at room temperature and contains long chains of fatty acids, e.g., Animals fat.
      

1. Lowering the activation energy by creating an environment in which the transition state is stabilized (e.g. straining the shape of a substrate-by binding the transition-state conformation of the substrate/ product molecules, the enzyme distorts the bound substrate(s) into their transition state form, thereby reducing the amount of energy required to complete the transition).
2. Lowering the energy of the transition state, but without distorting the substrate, by creating an environment with the opposite charge distribution to that of the transition state.
3. Providing an alternative pathway: For example, temporarily reacting with the substrate to form an intermediate ES complex, which would be impossible in the absence of the enzyme.
4. Reducing the reaction entropy change by bringing substrates together in the correct orientation to react. Considering AHỊ alone overlooks this effect.
5. Increases in temperatures speed up reactions. Thus, temperature increases help the enzyme function and develop the end product even faster. However, if Sheated to heated too much, the enzyme's shape deteriorates and only when the temperature comes back to normal does the enzyme regain its shape. Some enzymes like thermolabile enzymes work best at low temperatures.

The catalytic cycle of an enzyme action can be described in the following steps:

1. First, the substrate binds to the active site of the enzyme, fitting into the active site.
2. The binding of the substrate induces the enzyme to alter its shape, fitting more tightly around the substrate.
3. The active site of the enzyme, now in close proximity of the substrate breaks the chemical bonds of the substrate and the new enzyme- product complex is formed.
4. The enzyme releases the products of the reaction and the free enzyme is ready to bind to another molecule of the substrate and run through the catalytic cycle once again.

1. DNA or deoxyribonucleic acid is a helically twisted double-chain polydeoxyribo- nucleotide macromolecule.
2. The two strands of DNA run anti-parallely to each other called as DNA duplex.
3. The spiral twisting of DNA has two types of alternate grooves, i.e., major and minor.
4. One turn of 360° of the spiral has about 10 nucleotides on each strand of DNA occupying a distance of about 3.4 nm.
5. The nucleotides within each strand are held together by the phosphodiester bonds between the 5' carbon of one nucleotide and the 3' carbon of the adjacent nucleotide. This strong covalent bond holds the sugar/phosphate backbone together.
6. The two strands of DNA are held together by weak hydrogen boiias between the nitrogenous bases. These hydrogen bonds are base specific. That is adenine forms 2hydrogen bonds with thymine CA=T and cytosine forms 3 hydrogen bonds with guanine (C=G).
7. As specific and different nitrogen bases occur on two DNA chains, they are said to be complementary, i.e., urine lies opposite to pyrimidine. This purine-pyrimidine pairing also contributes to the thickness of strand, i.e., 2nm, and makes the two chains complementary.​​​​​​

1. Rakesh would pick T and U cards as thymine is present only in DNA and uracil is present only in RNA.
2. Uracil does not form H-bonding with other nucleic acid as uracil is found in RNA and RNA is single-stranded molecule.
3. A nucleic acid is a polymer of nucleotides which is composed of three components.

• Heterocyclic compound-nitrogen base (adenine, guanine, uracil, cytosine and thymine). The skeletal heterocyclic in DNA/ RNA is called as purine and pyrimidines. Adenine and guanine are purines while uracil (only in RNA), thymine (only in DNA) and cytosine are pyrimidines.
• Monosaccharide (ribose or deoxyribose).
• Phosphoric acid or phosphate.

In living systems, metabolism involves two following types of pathways.

1. The anabolic pathway is called biosynthetic pathway. It leads to a more complex structure from a simpler structure, e.g., the pathway involving the conversion of acetic acid into cholesterol. These pathways consume energy.

2. The catabolic pathway leads to simpler structure from a complex structure, e.g., thepathway involving conversion of glucose into lactic acid in our skeletal muscles. This pathway leads to the release of energy, e.g., energy is liberated when glucose is degrated to lactic acid in our skeletal muscles.

1. Amino acids are the building blocks of proteins.
2. Besides building blocks of proteins, amino acids are involved in the synthesis of a number of compounds such as hormones, amine buffers, antibiotics, prokaryotic cell wall, etc.
3. Such pills might be harmful in long run and one should have balanced diet and exercise regularly to built muscles naturally.
4. Vikas's teacher was concerned about his students health, and knows scientific ethics and had knowledge about harmful effects of such products.